1. Field of the Invention
The present invention relates to a load control system and, more particularly, to a system for providing centralized monitoring and/or control for a plurality of loads such as luminaire loads (lighting fittings) and the like.
2. Description of the Prior Art
The disclosure of Japanese Laid-open Patent No. 7,587/1981 is hereby incorporated as the prior art by reference. FIG. 1 shows the schematic diagram of the prior art load control system illustrated in said literature, wherein, 1 denotes a power line, 2 denotes a plurality of luminaire loads connected thereto, 3 denotes a plurality of terminal units for providing ON-OFF control of the plurality of luminaire loads 2 with the use of switching devices such as relay contacts and the like, and 4 denotes a central control unit to send out control signals to terminal units 3 for the control of luminaire loads 2 via a signal transmission line 5 whereby a specific address is assigned respectively to each terminal unit 3.
According to the prior art system, a load control signal transmitted first from the central control unit 4. This load control signal is consists of a base band or a modulated pulse train, more specifically, of a series of address pulses having an address data for specifying a required terminal unit 3 and a series of control pulses having a control data for controlling the respective luminaire load 2 which is connected to the selected terminal unit 3. Each terminal unit 3 monitors a load control signal which is transmitted through the signal transmission line 5 and accepts the load control signal if the address data thereof coincides with own address. The terminal unit 3 then decodes the control data contained in the accepted signal and provides the required control of the luminaire load 2 in accordance with the decoded control data through the use of relay contacts and the like. Further, there is provided a monitor input terminal (not shown) with each of the terminal units 3, and a signal indicating the status of each luminaire load 2 which is connected to the respective terminal unit 3 is fed to this monitor input terminal. The signal indicating the status of the luminaire load 2 is transmitted to the central control unit 4 as monitor input pulses together with address pulses indicating the address of the terminal unit 3 and address pulses indicating the address of the central control unit 4. The status of each luminaire load 2 is monitored at the central control unit 4 by receiving the monitor input pulses.
FIG. 2 is a diagram illustrating the luminaire load control system of the prior art being installed in a building facility together with an electric power unit. Branch power lines 1a-1d of the main power line 1 are branched through 20 A rating breakers 6a-6d. According to the law or private regulations such as an electric installation engineering standard, the capacity at the final end of the power line is specified to 20 A when the luminaire loads are fluorescent lamps. Connected to each branch power line through a terminal unit are luminaire loads. For instance, luminaire loads 2a-2c are connected to a branch power line la through a terminal unit 3a. Generally, in an ordinary building facility, a plurality of breakers 6a-6d are installed in an electric power room as one unit of a distribution board for centralized control. That is, the branch power lines 1a-1d are branched from the electric power room by every 20 A electric current capacity in a star connection. On the other hand, every terminal unit 3a-3p is installed in the ceiling in proximity to its respective luminaire load in order to shorten the wiring thereto and a signal transmission line 5 is connected to the terminal units 3a-3p in a transition connection whereby the terminal units are connected in series. As is described above, according to the prior art system, the breakers 6a-6d and the central control unit 4 are gathered for centralized monitor and control.
The disclosure of Japanese Laid-open Patent No. 64,140/1988 is hereby incorporated by reference in FIG. 3 as another prior art load control system. Now referring to FIG. 3, branch power lines 1a-1d are branched from the main power line 1. Connected to the respective branch power lines are a plurality of luminaire loads 2a1-2d2, a plurality of control terminals 3a1-3d2 which are connected to respective luminaire loads for providing ON - OFF control thereof by utilizing switching means such as relay contacts and the like, a plurality of control means made up of operation command input terminals 4a1-4d2 for operating the control terminals, central control units 4A-4B for sending out control signals to said control terminals 3a1-3d2 upon receipt of signals from said operation command input terminals 4a1-4d2 corresponding to the branch power lines 1a-1d, and block filters 7 for providing the isolation of a signal for power line carrier communication between the main power line 1 and the branch power lines 1a-1d.
According to this type of load control system, in case of controlling a luminaire load 2 being connected to a different branch power line, for instance, in case of controlling the luminaire load 2a1 being connected to the branch power line 1a from the operation command input terminal 4d1 connected to the branch power line 1d, the flow of the control is as follows. First, an operation command is transmitted from the operation command input terminal 4d1 to the central control unit 4B through the branch power line 1d in power line carrier communication mode. Second, the central control unit 4B then transmits the information in the power line carrier communication mode to the central control unit 4A being connected to the branch power line 1a, which is connected to the control terminal 3a1 to be controlled, via the main power line 1 in accordance with the contents of the received command. Thirdly, the central control unit 4A which has received the information sends out the operation command through the branch power line 1a to the control terminal 3a1. Finally the luminaire load 2a1 is controlled by the control terminal 3a1 under the received operation command with use of switching means such as relay contacts.
As mentioned above, numerous prior art systems for controlling luminaire loads have been proposed and these systems essentially utilize two line systems in wiring, a power line system and a signal transmission line system, which has resulted in expensive installation and required wire checking for each line system in case of failure. In order to check every terminal unit when the signal transmission line system is out of order, for example, the checking has to be done by turning off the power to the power line system for the loads which are under the control of the terminal units to which the signal transmission lines are wired. Particularly, in the case of a single signal transmission line being wired to a plurality of terminal units which are in connection with a plurality of power lines, all of the power lines have to be powered off during the checking period of time. As is clear from the above, there have been many problems in the maintenance of the prior art system, such as in its complexity and the difficulty of checking failures.
It is therefore an object of this invention to solve such problems and to provide a load control system with less wiring and which is easy to maintain.
It is another object of this invention to provide a load control system wherein the maximum time required for a central control unit to detect a failure of a terminal unit is shortened and an amount of traffic through signal transmission lines is considerably decreased.
It is still another object of this invention to provide a load control system wherein an amount of traffic through power lines is decreased by making the reciprocity control possible between terminal units connected on a different branch power lines for hastening the control of loads and improving the reliability.